Graphite and carbon materials, especially reinforced carbon-carbon composite substrate materials, are subject to many applications in modern industry, particularly in the aerospace and aviation fields. However, such materials, when unprotected, are subject to degradation at elevated temperatures. Since many applications involve high temperatures, resistance to high temperature and thermal shock are often required properties of the material.
Reinforced carbon-carbon composite substrates are generally constructed of fibers and bound by carbon matrix, resulting in a material having excellent structural properties. Generally, precursors for carbonaceous fibers such as polyacrylonitrile, rayon or pitch-based fibers are utilized. Carbon-carbon impregnation materials generally are phenolic, furfuryl or pitch-based materials. However, the use of a specific impregnation or substrate material is not a limitation upon the present invention.
Graphite and carbon materials, including reinforced carbon-carbon composites, are subject to degradation, such as oxidation, when utilized in high temperature environments in the presence of oxygen. Generally, an unprotected graphite or carbon material will begin to oxidize at temperatures in excess of about 650.degree. F. in air. Therefore, in order to effectively utilize these materials in high temperature applications, it is necessary to provide protection from degradation, including oxidation. Accordingly, a need exists for a protective coating suitable for use on graphite and carbon materials, and especially for reinforced carbon-carbon composite materials, where such materials are subject to temperatures ranging from about 650.degree. F. to about about 4100.degree. F.
Various types of sputtering techniques are known to those skilled in the art. For example, sputtered oxide coatings for airfoil applications and sputter deposited multilayered ceramic-metal coatings are described respectively in a paper entitled "Improvement of Sputtered Oxide Coating Adherence and Integrity for Turbine Airfoil Applications" by M. A. Bayne, R. Busch, J. W. Fairbanks and J. W. Patten and in a paper entitled "Development of Sputter Deposited Multilayered Ceramic/Metal Coatings" by J. W. Patten, R. W. Moss, M. A. Bayne, D. D. Hays and E. D. McClanahan, both papers presented in the "Proceedings of the First Conference on Advanced Materials for Alternative Fuel Capable Directly Fired Heat Engines" in Castein, Maine on July 31-Aug. 3, 1979, and published by the U.S. Department of Energy, December 1979, CONF-790749. These references are hereby incorporated by reference and relate to the use of certain sputtered coatings on metallic substrates.